Module III Flashcards
- Describe the oestrous cycle/ovarian cycle of rodents and describe how pheromones can affect the ovarian cycle and pregnancy
Ovarian 4-5 day cycle - spontaneous ovulation. The female has an estrous cycle and she will only allow mating during estrous. The morning after the mating has taking place, there will be a vaginal plug left by the sperm secretion by the male.
Pheromones and ovarian cycle:
● Lee-Boot effect: Female mice that are housed together without scent stimulation from a male, their oestral cycle will become slower and will eventually stop completely in anoestrus.
● Whitten effect: Female mice that are kept without male mice nearby are an-oestral (the Lee–Boot effect). If the females are exposed to pheromones from male mice’s urine, their oestral cycle will start again. This can be exploited to synchronize oestrus in female mice. If the female mice are put together with the male on the third day after having been exposed to male mouse scent/pheromones, approximately 75% of the females will be mated the following night.
● Bruce effect: insufficient implantation of the fertilized egg or abortion if a pregnant female is exposed to scent stimulation (e.g. urine) from an unfamiliar male. This is important because researchers would have to change gloves between handling different pregnant mice from different strains.
● Wanderberg effect: Young female mice appear to become sexually mature more quickly when a male mouse is nearby as the male pheromones will stimulate the maturing
- Describe the rodents’ senses of hearing, vision and olfaction and discuss the importance of being aware of how these senses differ between rodents and humans
Vision - rodents have low acuity vision so can see quite blurry. Humans are trichromatic so we have the three photoreceptors blue-ish, greenish and red-ish allowing us to utilize light from app. 400 nm to 700 nm. Mice and rats are dichromatic, they have only two classes of photoreceptors, namely ultraviolet and greenish. Speculation that mice can feel stressed if deprived of uv light as they are kept under fluorescent light tubes which is an unnatural source of light for these rodents. Because their vision is bad, they use their whiskers to navigate in the darkness.
Olfaction - mice have a highly developed sense of smell and it is important for communication. Pheromones are chemical substances released by an animal to signal something to another animal and they are found in urine, feces and saliva. This chemical communication can be used to identify other mice (sex, age, status etc) and to decide on how to approach/interact.
Hearing - The sense of hearing is highly developed in mice and rats and their hearing range is well into the ultrasonic frequencies, which starts at 20 kHz. Humans are not able to hear ultrasound and therefore we are not able to hear a large part of rodent communication nor many of the sounds that may stress rats and mice. Rats also use ultrasonic vocalization for navigating in the dark, they emit very fast “clicks” and use the reflections from the surrounding to navigate in total darkness. It is unknown whether mice also do the same.
- Discuss what temperature is optimal for mice, how the preference for a specific temperature can be established and how mice can thermoregulate
Mice and rats are homeotherm and able to maintain a stable internal body temperature regardless of external influence. Mice especially will regulate their temperature both via internal homeostasis regulation and by for example nest building. In standard laboratory environments mice are housed at 20–24 °C. However, their thermoneutral zone ranges between 26 °C and 34 °C and the lower critical temperature for a single-housed mouse with no nesting material is 34 °C. Such a challenge to homeostasis is by definition stressful, and could therefore affect many aspects of physiology and behavior.
Mice preferred warmer temperatures only for maintenance and inactive behavior and this effect was most pronounced in females. Therefore, it is important to provide mice with the opportunity to thermoregulate by nesting.
Mice are extremely efficient nest builders and it has been shown that mice – provided with an adequate and sufficient amount of nesting material such as cotton wool – are able to build a nest in which the temperature is more than 30 °C even though the temperature outside the nest is below 0 °C.
- Give examples of stressors (i.e. any adverse stimulus; physical, mental, emotional, internal or external, that tends to disturb the homeostasis of an organism) and discuss the physiological consequences and manifestations of stress in rodents
Stress will be defined as the sum of the biological reactions to any adverse stimulus - physical, mental or emotional, external or internal- that tends to disturb the homeostasis of an organism. If this becomes chronic and the animal is not able to cope then it is known as distress. Many procedures and environmental factors may elicit fear, pain or other stressful conditions in the animals. Fear and pain will of course affect animal behavior and stressful conditions will affect for example the immune system, the cardiovascular system and reproduction and the last decades of research has shown that barren cage environments will result in animals with physiological, immunological, neurological and behavioral abnormalities.
Examples of stressors include restraint/immobilization, social defeat stress, lights on overnight, social isolation/crowding, aversive smells, tests like the forced swim test, corticosterone, wet/no bedding, etc.
- Discuss how different handling methods of mice can affect animal welfare and animal behaviour
There are three main forms of mice handling: tail handling, tunnel handling, and cupping. According to the NC3Rs website, using a tunnel or cupped hand to pick up mice causes less anxiety than traditional tail handling. Mice quickly habituate to tunnel handling and can subsequently be restrained by the scruff or tail base for procedures or health and welfare assessments without negating the positive impacts of the non-aversive capture. Picking up mice by the tail can impact on scientific outcomes, with mice handled by tunnel and cupping methods showing improved performance in behavioural tests.
